Scilab Function
Last update : 12/1/2004

tf2des - transfer function to descriptor

### Calling Sequence

  `S=tf2des(G)`
  `S=tf2des(G,flag)`

### Parameters

- `G`: linear system (`syslin` list) with possibly polynomial `D` matrix
- `flag`: character string `"withD"`
- `S`: list

### Description

Transfer function to descriptor form: `S=list('d',A,B,C,D,E)`

      E*xdot = A*x+B*u
      y = C*x + D*u

Note that `D=0` if the optional parameter flag=`"withD"` is not given. Otherwise a maximal rank `D` matrix is returned in the fifth entry of the list `S`

### Examples

    s=poly(0,'s');
    G=[1/(s-1),s;1,2/s^3];
    S1=tf2des(G);des2tf(S1)
    S2=tf2des(G,"withD");des2tf(S2)

### See Also

`pol2des`, `tf2ss`, `ss2des`, `des2tf`,